1. Field of the Invention
The present invention relates generally to computer-assisted design of vehicles and, more specifically, to a system and method of interactive evaluation and manipulation of a geometric model in the computer-assisted design of a vehicle.
2. Description of the Related Art
Vehicle design, and in particular the design of an automotive vehicle, has advanced to a state in which computer-assisted design techniques are frequently incorporated in the development of a new vehicle or redesign of an existing vehicle. Enhanced visualization software tools allow for interactive display and manipulation of large geometric models, including models developed using computer aided design (CAD). In the field of vehicle design, the use of computer aided design and visualization techniques are especially beneficial in designing, packaging, and assembling the various systems incorporated within the vehicle to maximize the design and functional capabilities of these vehicles. Advantageously, potential vehicle system designs can be considered in a timely and cost-effective manner by analyzing a digital representation of a proposed design versus preparing an actual vehicle model.
One aspect of the design task for a vehicle is the coexistence of a CAD generated geometric model and a physical model. An advantage of the physical model is that it provides a physical representation of the design that can be evaluated visually and by touch. For example, a clay model allows a designer to assess a surface quality of the model through multi-fingered, two handed, dexterous manipulation of the model. Designers often trace the contour of a vehicle surface with their fingertips and palm to obtain tactile information to assess surface fairness. A disadvantage of the physical model relates to transforming the physical model back into the original CAD format after the designer has modified the physical model.
The geometric model of a proposed design is typically constructed using a technique such as computer-aided design (CAD). An advantage of a CAD model is that known mathematical tools, such as computer-aided engineering (CAE), are available to constrain and guide the designer in evaluating the design. In addition, the construction steps involved in creating the geometric model can be recorded for later use. The geometric model can easily be updated using the construction steps in light of a new set of parameters. A disadvantage of a CAD model relates to viewing a 3-dimensional model in 2-dimensions on a display device.
Recently, designers have utilized virtual reality simulation techniques to provide a bridge between the physical model and the CAD model. Virtual reality allows a user to interact with a virtual environment, including a virtual object in the virtual environment, as if the user was actually immersed in the virtual environment. It should be appreciated that a virtual object within the virtual environment may include a virtual surface.
A user-friendly physical device, such as a haptic device, serves as an interface between the user and the virtual environment. Advantageously, the haptic device reproduces at a high rate of speed the sensation of freely moving an object within a constrained environment by determining the forces exchanged between the interacting geometries. This process is frequently referred to as haptic rendering. An example of a haptic device is disclosed in U.S. Pat. No. 5,694,013 to Stewart et al., entitled xe2x80x9cForce Feedback Haptic Interface for a Three-Dimensional CAD Surfacexe2x80x9d, the disclosure of which is incorporated by reference.
Haptic rendering provides the user with information regarding the virtual surface using force feedback from a single point of contact. In particular, haptic browsing refers to the tactile interaction and visualization of the geometric surface using a haptic interface. An example of a methodology of haptic browsing is disclosed in U.S. Pat. No. 5,844,392 to Peurach et al., entitled xe2x80x9cHaptic Browsingxe2x80x9d, the disclosure of which is incorporated by reference. While the method disclosed by Peurach et al. ""392 uses haptics to present information regarding a single point, it does not constrain the haptic interface to the surface of the geometric model to convey kinesthetic or tactile information.
Haptic sculpting is a recent technique providing a bridge between a geometric model and a physical prototype. In haptic sculpting, a user manipulates a free-form surface in the geometric model, similar to a designer using a tool to modify the shape of the surface of a physical model. A designer working with a CAD model typically moves a control point on a free form surface, such as a NURBS surface, back and forth until the desired geometric properties are obtained. Examples of geometric properties include fairness, smoothness and C0, C1, and C2 continuity, as is known in the art. However, to achieve the desired shape, the designer still needs to alternate back and forth between different control points as changes ripple across the surface due to the mathematical properties of free-form surfaces. Preferably, haptic sculpting allows a user to sculpt an entire section of the surface with a single sweeping motion, continuously and autonomously changing the set of controlled control points, so as to achieve the desired sculpted form of the surface.
Previous haptic sculpting approaches have not constrained the haptic interface to the virtual surface and the virtual surface to the haptic interface during exploration and manipulation of the surface. Thus, there is a need in the art for a system and method of interactive evaluation of a geometric model using a haptic interface constrained to follow a surface contour of a virtual surface within the virtual environment, while the surface is simultaneously constrained to follow the user""s motion.
Accordingly, the present invention is a system and method of interactive evaluation and manipulation of a geometric model. The system includes a computer system having a memory, a processor, a user input device and a display device. The system also includes a computer generated geometric model stored in the memory of the computer system. The system further includes a haptic interface operatively in communication with the computer system, wherein the haptic interface includes a haptic end effector device for transmitting information between a user and the geometric model as the user browses or edits the surface of the geometric model using the haptic end effector device.
In addition, the present invention is a method of interactive evaluation and manipulation of a geometric model including the steps of browsing a surface of the geometric model using a haptic end effector device, determining if a user is signaling to edit the surface of the geometric model, and continuing to browse the surface of the geometric model if the user is not signaling to edit the surface of the model. The method also includes the steps of editing the surface of the geometric model if the user is signaling to edit the surface of the geometric model, determining and mapping a haptic end effector device position on the surface of the geometric model while editing, and identifying a closest point to edit on the surface of the geometric model to the haptic end effector device position. The method further includes the steps of editing a fixed point by determining a surface position and property of the closest point, and modifying the geometry of the surface until the closest point converges on the haptic end effector device position, and editing a non-fixed point by decomposing the haptic end effector device position into editing and browsing components. The method includes the steps of finding a new surface position on the geometric model using a previous surface position and haptic end effector device position, and modifying the geometry of the surface until the closest point converges on the haptic end effector device position. The method still further includes the steps of editing a surface property in the neighborhood of the closest point and determining and applying a stick-to-surface/stick-to-pen force and a property feedback force using the surface property in the neighborhood of the closest point to control a location and force output of the haptic end effector device.
One advantage of the present invention is that a system and method of interactive evaluation and manipulation of a geometric model is provided that constrains a user""s motion to stick to a surface of a geometric model, while simultaneously controlling the surface to stick to the device. Yet another advantage of the present invention is that a system and method is provided for haptically browsing and editing the surface of the virtual model, thus allowing the user to assess a physical property of a surface, and/or manipulate the shape of the surface. Still another advantage of the present invention is that a system and method is provided that bridges between the physical model and the CAD model by allowing the user to touch and manipulate the CAD model using virtual reality technology. Still yet another advantage of the present invention is that the system and method integrates tactile feedback in a force enabled simulation to constrain physical interaction of the user to the virtual model and further constrain the model to the haptic device. A further advantage of the present invention is that the motion of the user is constrained to the virtual surface representing the geometric model to provide the user with an enhanced understanding of the geometric properties of the model. Still a further advantage of the present invention is that the user can simultaneously explore and shape the local surface properties of the geometric model, by constraining the haptic device to follow the surface contour while simultaneously manipulating the surface to follow the user""s motion.